The Big Mac has been one of McDonald’s most popular sandwiches for over 50 years. Initially created to compete with the Big Boy Double Decker Burger, it went nationwide in 1968. The sandwich was an immediate hit. Known for its catchy jingle in the 1970s and its secret sauce, the Big Mac, has never left the menu. There have been variations throughout the years, but next week, McDonalds in the US will debut a new version already popular in Europe, the Chicken Big Mac. Just take away the burger patties and replace them with McChicken patties…